The present invention relates to engines and exhaust after treatment systems and, more particularly, to methods and apparatus for determining whether diesel particulate filter (DPF) regeneration is too frequent.
Modern diesel engines are ordinarily provided with DPFs to filter particulate matter such as unburned hydrocarbons in the engine exhaust. As soot collects in a DPF, it becomes necessary to remove the soot, ordinarily by a process referred to as regeneration. There are two primary mechanisms employed for regeneration: oxidation of soot by O2 ((C+O2→CO2) and/or (2C+O2→2CO)) called O2-based regeneration and oxidation of soot by NO2 ((C+2NO2→CO2+2NO) and/or (C+NO2→CO+NO)) called NO2-based regeneration. U.S. patent application Ser. No. 12/864,328, entitled “METHOD AND APPARATUS FOR REGENERATING A CATALYZED DIESEL PARTICULATE FILTER (DPF) VIA ACTIVE NO2-BASED REGENERATION WITH ENHANCED EFFECTIVE NO2 SUPPLY”, and U.S. patent application Ser. No. 12/864,330, entitled “METHOD AND APPARATUS FOR NO2-BASED REGENERATION OF DIESEL PARTICULATE FILTERS USING RECIRCULATED NOX” both of which are incorporated by reference, describe using modeling to calculate soot load in a DPF. Regeneration by O2 is typically referred to as “active” regeneration as it ordinarily involves the addition of heat to burn off soot that has collected in the DPF, although some O2 regeneration often occurs during normal operation of the engine and exhaust after treatment system (EATS). Regeneration by NO2 is typically referred to as “passive” regeneration and is the primary mechanism by which the DPF is continuously regenerated during normal operation of the engine and EATS.
Soot accumulation in the DPF is affected by engine-out soot as well as by catalytic activity of EATS components such as diesel oxidation catalysts (DOCs) and DPF catalysts, as well as by factors such as engine exhaust temperature and NOx levels. Under many operating conditions, such as during normal highway operation of a truck having a diesel engine, passive regeneration can prevent substantial soot build-up in a DPF, and may avoid the need for active regeneration altogether. Under less favorable conditions, such as local operation at unfavorable exhaust temperatures, soot builds up in the DPF and an active regeneration must be performed.
One way of determining whether an active regeneration is necessary is by measuring pressure drop across the DPF and estimating soot load as a function of the pressure drop at the particular exhaust temperature and exhaust mass flow rate at which the engine is being operated. If this pressure drop soot load estimate exceeds a predetermined soot load limit, an active regeneration will be initiated.
The inventors have recognized that too frequent regeneration may be indicative of a problem, ordinarily a problem associated with either excessive soot generation by the engine or inadequate catalytic activity by the DOC, although other factors such as inadequate catalytic activity by the DPF or reduced DPF effective volume (such as when the DPF is filled with ash) may also or alternatively be behind frequent regenerations. Failure to identify such problems can lead to catastrophic engine or catalyst failures.
Currently, whether regeneration is occurring too frequently is determined by comparing the frequency of regeneration with a predicted regeneration frequency, i.e., a specific time interval. However, as noted, under certain conditions, a truck may not need any regeneration while, under other conditions, the same truck may need a regeneration every few days. This variation makes it difficult to use a single or particular time interval criteria to define what normal DPF regeneration frequency is because a particular interval may be too frequent for a truck operated primarily on the highway, while being normal or too infrequent for a truck operated in stop-and-go traffic.
It is desirable to provide a method and apparatus the can reliably facilitate detection of whether DPF regeneration is occurring too frequently. It is further desirable to provide such as method and apparatus that involves the use of minimal additional equipment. In addition to reasons relating to avoiding engine or catalyst failures, it is desirable to detect excessive DPF regeneration to comply with regulations such as California Code of Regulations: CCR 1971.1 (e)(8.2.2) Frequent Regeneration, Code of Federal Regulations: CFR Part 86.010-18 paragraph (g)(8)(ii)(B) DPI Regeneration Frequency. 
According to an aspect of the present invention, a method is provided for detecting abnormally frequent diesel particulate filter (DPF) regeneration. The method comprises measuring a pressure drop across the DPF and using the measured pressure drop to calculate a pressure drop based soot load estimate, calculating soot output from an engine model and using the calculated soot output to calculate an emissions based soot load estimate, comparing the pressure drop based soot load estimate with the emissions based soot load estimate, and providing a warning if a difference between the pressure drop based soot load estimate and the emissions based soot load estimate exceeds a predetermined value.
According to another aspect of the present invention, a method is provided for detecting possible diesel engine malfunction or diesel oxidation catalyst (DOC) malfunction. The method comprises measuring a pressure drop across a diesel particulate filter (DPF) and using the measured pressure drop to calculate a pressure drop based soot load estimate, calculating soot output from an engine model and using the calculated soot output to calculate a emissions based soot load estimate, comparing the pressure drop based soot load estimate with the emissions based soot load estimate, and checking functionality of the diesel engine and the DOC malfunction if a difference between the pressure drop based soot load estimate and the emissions based soot load estimate exceeds a predetermined value.
According to another aspect of the present invention, a diesel engine with an exhaust after treatment system is provided and comprises the diesel engine, the diesel engine comprising an exhaust, a diesel oxidation catalyst (DOC) downstream of the diesel engine exhaust, a diesel particulate filter (DPF) downstream of the DOC, sensors for measuring a pressure drop across the DPF, and a controller. The controller is arranged to arranged to calculate a pressure drop based soot load estimate based on the measured pressure drop, calculate an emissions based soot load estimate based on soot output calculated from an engine model, compare the pressure drop based soot load estimate with the emissions based soot load estimate, and provide a warning if a difference between the pressure drop based soot load estimate and the emissions based soot load estimate exceeds a predetermined value.
According to another aspect of the present invention, a warning system for diesel engine with an exhaust after treatment system is provided, the exhaust after treatment system comprising a diesel oxidation catalyst (DOC) downstream of an exhaust of the engine and a diesel particulate filter (DPF) downstream of the DOC. The warning system comprises sensors for measuring a pressure drop across the DPF, and a controller arranged to calculate a pressure drop based soot load estimate based on the measured pressure drop, calculate an emissions based soot load estimate based on soot output calculated from an engine model, compare the pressure drop based soot load estimate with the emissions based soot load estimate, and provide a warning if a difference between the pressure drop based soot load estimate and the emissions based soot load estimate exceeds a predetermined value.